A rubber O-ring 51 made of an FFKM rubber or an FKM rubber provided with a resistance characteristic against plasma has been conventionally used in a seal portion of an apparatus using plasma in an apparatus for manufacturing a semiconductor such as etching, ashing, plasma CVD or the like, as shown in FIG. 7. The apparatus mentioned above is structured such as to manufacture a semiconductor device by irradiating the plasma. Since the irradiation of the plasma is executed under a vacuum atmosphere, it is necessary to shut off an inner portion of the apparatus from an atmospheric pressure. Accordingly, the plasma resistant seal is used for this object.
However, since energy of the plasma is very strong, even the O-ring 51 made of the rubber such as the FFKM, the FKM or the like provided with the resistance characteristic is scraped due to an influence of the plasma as shown in FIG. 8, and is lost in some cases, so that there is a case that a sealing function is lowered. Further, since the lost O-ring piece forms a foreign material so as to produce a particle of the semiconductor device, there is a case that a function of the semiconductor device is significantly lowered. In particular, in recent years, a plasma condition in manufacturing the semiconductor becomes gradually severe (a plasma frequency is increased), and it is required to develop a seal which is excellent in both of a plasma resisting performance and a sealing performance so as to correspond to this matter. Further, on the basis of the seal structure constituted by a single unit of the O-ring 51 mentioned above, there is a risk that the O-ring 51 protrudes to a gap 52 in a vacuum side so as to be damaged.
Further, there is a case that a seal made of a polytetrafluorethylene (PTFE) is employed as a structure having the resistance characteristic against the plasma, in place of the rubber O-ring 51, however, since the PTFE is inferior to the FFKM and the FKM in a performance as an elastic body, a sealing performance against the atmospheric pressure is not so good.
Further, as the plasma resistant seal, there have been conventionally known a structure described in Japanese Unexamined Patent Publication No. 2002-161264, and a structure described in Japanese Unexamined Patent Publication No. 2000-34466. However, these prior arts are structured such that a composition structure of the rubber seal is improved for the purpose of improving the plasma resisting performance, and are not provided with a plasma seal in a plasma side of a main seal rubber packing as are different from the present invention.
Taking the above matters into consideration, an object of the present invention is to provide a plasma resistant seal which is excellent in both of a plasma resisting performance and a sealing performance, and can prevent a packing/O-ring from protruding to a gap in a vacuum side.